1. Field of the Invention
The present invention relates to a fluid apparatus of an internal gear type for operating as a fluid pump or a fluid motor, said apparatus comprising; an internally toothed gear rotatively mounted within a housing, an externally toothed gear disposed within said internally toothed gear so as to mesh therewith, and a crescent-shaped partition piece disposed within the housing between both gears.
2. Description of Related Art
FIG. 1 illustrates a front view of an internal gear pump of the present invention as an embodiment of a fluid apparatus in which a cover is removed. An internal gear 3 having internal teeth 2 is rotatively mounted in a housing 1. An external gear 5 having external teeth 4 meshed with the internal teeth 2 is fixed to a driving shaft rotatively supported in the housing 1 and is disposed eccentric to the internal gear 3. A crescent-shaped partition piece 6 is disposed at a space between both gears. The housing 1 is provided with an outlet port 7 and an inlet port 8 at positions before and after the meshing point of both gears, respectively.
With this arrangement the external gear 5 driven by rotation of the driving shaft causes the internal gear 3 to rotate whereby a bite gap at the side of the outlet port between the internal teeth 2 and the external gear 4 is gradually reduced so that the fluid existing between the gears is discharged from the outlet port 7 to the outside of the housing while the gap at the side of the inlet port is gradually increased so that fluid is absorbed into the gap from the inlet port 8 according to a negative pressure built-up in the gap.
In such an internal gear pump the following matters are generally known as a basic design technique of both gears 3 and 5.
Firstly, the meshing tooth profile of both gears of such an internal gear pump is usually determined only by their meshing relation so that once the tooth profile of one of the gears is determined, the tooth profile of the other gear is defined in only one meaning manner and in such a manner that the both gears mesh in rolling contact without slippage along the intermeshing pitch circles, and a meshing rate is larger than 1. Such an arrangement realizes smooth rotation of the gears 3 and 5, and prevents wear of tooth surfaces and noise.
Secondly, when both gears 3 and 5 mesh with each other as shown FIG. 2, the volume of a confined space 11 between two meshing points 9 and 10 of the teeth 2 and 4 is reduced to a minimum as shown FIG. 2 during rotation of the gears 3 and 5 before the volume of the space is increased. Therefore, the adjacent edges 7a and 8a of the outlet port 7 and the inlet port 8 are usually positioned nearby the meshing points 9 and 10, respectively, which make the volume of the confined space 11 minimum so as to prevent pulsation of the fluid discharging pressure or cavitation upon absorption.
On the other hand, addition to the matter that the meshing rate is larger than 1, the tooth profile is generally so determined that both meshing points 9 and 10 are involved in the tooth surface at the rotational position where the volume of the confined space 11 becomes minimum, and thus effective tooth surfaces for meshing of such gears 3 and 5 are present in a higher height to the inside or the outside from the respective intermeshing pitch circles 12 and 13, respectively.
Furthermore in such an internal gear pump having a crescent-shaped partition piece, the relative curvature between the two tooth surfaces and operating pressure angle are so taken into consideration that they may be as small as possible whereby the load applied to the tooth surfaces can be reduced and wear of the tooth surfaces and bearings can be prevented.
By the way, such a consideration for the relative curvature and operating pressure angle in such an internal gear pump is very important especially near the end of meshing of both gears and when the distal end of the tooth of the external gear and the proximal end of the tooth of the internal gear are meshed with each other. That is because, as diagrammatically shown in FIG. 3, the torque required for rotating the internal gear 3 against pressures P1 and P2 applied to the internal tooth 2 is not constant over the whole meshing region between the internal tooth 2 and the external tooth 4, but the torque can be increased as the biting point 14 is moved from the distal end of the internal tooth 2 of the internal gear 3 to the proximal end thereof, and the load applied to the tooth surfaces might be maximum when both gears 3 and 5 mesh with each other at the distal end of the external tooth 4 and the proximal end of the internal tooth 2.
Furthermore, in such an internal gear pump by reducing the number of the teeth and difference in the number of the teeth of both gears 3 and 5 and by enlarging the tooth depth thereof, discharging volume can be large at the same outline size, and an outline size required for obtaining a desired output can be small. However, in such selection interference of both teeth 2 and 4 or so-called trochoid interference could occur when the external tooth 4 leaves the tooth groove of the internal gear after ending to mesh between both gears 3 and 5.
As the tooth profile of teeth 2 and 4 of the internal gear 3 and external gear 4 of such a kind of an internal gear pump, an involute profile, a profile along a line equidistant from an inner cycloid and an arced profile of internal gear teeth 2 have been widely used.
However, as such prior art pumps are compared with the above mentioned basic matters of design, in case of the involute profile the path of contact is straight, and the operating pressure angle is constant over the whole meshing region, the operating pressure angle upon meshing between the distal end of the external tooth 4 and the proximal end of the internal tooth 2 is larger than in other tooth profiles, so that the load applied to the tooth surfaces may be larger, and the load applied to the bearings may also be larger, by which trochoid interference can easily occur. Therefore, it has a problem that the outer profile size of the pump is obliged to be large for obtaining a desired discharging output.
On the other hand, the profile along the line equidistant from the inner cycloid and the arced profile as a tooth profile of the internal tooth 2 have not such a problem. This is because in such profiles the path of contact 15 is, as shown in FIG. 2, curved convexly in a radially outward direction so as to entwine around the pitch circles 12 and 13 and at the outside of the pitch circles 12 and 13 the operating pressure angle A upon meshing between the distal end of the external tooth 4 and the proximal end of the internal tooth 2 is relatively small, and also trochoid interference can hardly occur.
However, such prior tooth profiles of the inner cycloid and the trochoid types have a disadvantage that the relative curvature between the meshing tooth surfaces of the distal end of the external tooth 4 and the proximal end of the internal tooth 2 is relatively large so that in spite of merit of small pressure angle A and then reduction of the load applied to the tooth surfaces a relatively large tooth-contact stress can not be avoided.
The line equidistant from the inner cycloid as mentioned above is referred to as lines 19a, 19b and 19c, which as shown in FIG. 4 are spaced away from the respective inner cycloids 18a, 18b and 18c by a predetermined distance, respectively, said inner cycloids having different figures according to the respective size of inscribed circles 17a, 17b and 17c rolling along the intermeshing pitch circle 16, respectively. The inner cycloid is a straight line passing the center of the intermeshing pitch circle 16 and the equidistant line 19b is also a straight line parallel to the cycloid when the diameter of the rolling circle is equal to the radius of the intermeshing pitch circle 16. In case the diameters of rolling circles are smaller and larger than the radius of the intermeshing pitch circle 16, respectively, the respective inner cycloids 18a and 18b and the equidistant lines 19a and 19b are both curved lines, respectively. In this case the curving directions of the equidistant lines 19a and 19c are opposite to each other, so that the radius of curvature of the equidistant line 19a is smaller than the radius of curvature of the inner cycloid 18a by the amount of its equidistance while the radius of curvature of the equidistant line 19c is larger than the radius of curvature of the inner cycloid 18c by the amount of its equidistance.
Furthermore the radius of curvature of the curved inner cycloids 18a and 18c become smaller as they approach the intermeshing pitch circle 16, and become zero on the intermeshing pitch circle. Thus the radius of curvature of the curved equidistant line 19a is very small at the outside of the intermeshing pitch circle 16 while that of the equidistant line 19c is still relatively large even at the outside of the intermeshing pitch circle 16.
As a prior art, internal gear pumps employing the tooth profile of an equidistant line from an inner cycloid are known from Japanese Patent Application Publication Nos. 19767/75 and 1472/88. In the gear pump known from the former publication the tooth profile of its pinion is straight so that the diameter of the rolling circle is equal to the radius of the intermeshing pitch circle of the pinion. In the gear pump known from the latter publication the diameter of rolling circle is equal to the difference between the diameters of the internal gear and its pinion, and its diameter of the rolling circle is smaller than the radius of the intermeshing pitch circle. Thus in both gear pumps the diameter of the rolling circle is smaller than the radius of the intermeshing pitch circle of the internal gear. In the gear pump disclosed in Japanese Patent Application Publication No. 19767/75 the internal gear has an equidistant-line tooth profile from its inner cycloid described by the rolling circle whose diameter is smaller than the radius of the respective intermeshing pitch circle, and in the gear pump disclosed in Japanese Patent Application Publication No. 1472/88 both of the internal gear and pinion have an equidistant-line tooth profile from its inner cycloid, respectively. In the equidistant-line tooth profile the radius of curvature is, as mentioned above, small especially at the outside of the intermeshing pitch circle, so that the relative curvature between the tooth surfaces becomes large and thus the tooth-contact stress becomes also large when the distal end of the pinion and the proximal end of the internal gear mesh with each other.
Further if the diameter of the rolling circle is very small as shown in the pump of Japanese Patent Application Publication No. 1472/88, it would be difficult to make an equidistant-line tooth profile having a sufficient height toward the outside of the intermeshing pitch circle. In such a case by replacing the profile of the proximal end of the internal gear with an arced profile it is possible to make a tall tooth profile toward the outside of the intermeshing pitch circle. However, the tooth profile of the pinion meshed with the arced surface of the internal gear has a convex shape at the distal end thereof as the pinion of a so-called trochoid pump so that when the distal end of the pinion and the proximal end of the internal gear engage with each other, the relative curvature between the tooth surfaces also becomes larger due to meshing of the gear teeth having convex tooth profile of small radius of curvature.
And such a disadvantage is also the case even in an internal gear of an arced tooth profile in which the relative curvature between the meshing tooth surface upon meshing of the distal end of the pinion and the proximal end of the internal gear is relatively large.
The object of the present invention is to provided with a fluid apparatus of an internal gear type which avoids the disadvantages of the prior internal gear pumps as of type of an equidistant-line tooth profile from an inner cycloid and of an arced tooth profile type without losing their advantages, is less worn, less noisy, and more effective.